文章基本信息

标题：Regio- and stereoselectivity of various forms of purified cytochrome P-450 in the metabolism of benzo[a]pyrene and (-) trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene as shown by product formation and binding to DNA
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作者：J. Deutsch ; J. C. Leutz ; S. K. Yang 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1978
卷号：75
期号：7
页码：3123-3127
DOI：10.1073/pnas.75.7.3123
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Highly purified cytochromes P-450LM2 and P-450LM4 and partially purified P-450LM1, P-450LM3b, and P-450LM7 from rabbit liver microsomes exhibit different catalytic activities in the metabolism of benzo[a]pyrene (BzP) and (-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene [(-)trans-7,8-diol] in a reconstituted enzyme system. The two highly purified cytochromes also exhibit differences in the activation of BzP and (-)trans-7,8-diol to intermediates that bind to DNA, as well as in the stereoselective conversion of (-)trans-7,8-diol to the highly mutagenic and carcinogenic diol-epoxides r-7,t-8-dihydroxy-t-9,10-oxy-7,8,9,10- tetrahydrobenzo[a]pyrene (diol-epoxide I) and r - 7,t - 8 - dihydroxy - c - 9,10 - oxy - 7,8,9,10 - tetrahydrobenzo[a]pyrene (diol-epoxide II). P-450LM2 is more active than P-450LM4 in the metabolism of BzP and in its conversion to products that bind to DNA. In contrast, P-450LM4 is more active than P-450LM2 in the metabolism of (-)trans-7,8-diol and in its conversion to products that bind to DNA. The ratio of activity (percent substrate metabolized) with BzP relative to that with (-)trans-7,8-diol is 21 for P-450LM2 and 0.3 for P-450LM4; P-450LM1, P-450LM3b, and P-450LM7 gave intermediate ratios. Marked stereoselectivity in the oxygenation of the (-)trans-7,8-diol to the highly mutagenic and putatively carcinogenic diol-epoxides I and II was observed with P-450LM4, whereas the other preparations showed less selectivity. The ratio of diolepoxide I to diol-epoxide II ranges from 0.3 for P-450LM7 to 11 for P-450LM4. The substrate specificity and regio- and stereo-selectivity of the different forms of cytochrome P-450 may regulate the balance between activation and detoxification pathways of BzP and therefore determine the susceptibility of individual tissues, strains, and species to the carcinogenic action of BzP.
关键词：chemical carcinogenesis ; detoxification ; hydroxylases ; diol-epoxides ; benzo[ a ]pyrene activation